The thyroid hormones thyroxine (T4) and triiodothyronine (T3) play a significant role in the growth, development and differentiation of normal cells. The production of T4 and T3 is controlled by the thyroid-stimulating hormone (TSH), which is secreted by the hypophysis. An excess of circulating free T4 and T3, or both, is associated with the development of hyperthyroidism (e.g. Grave's disease).
Hyperthyroidism is a relatively common endocrine disorder in mammals and, particularly, in humans and cats. Typical hyperthyroidism treatments include chronic administration of an anti-thyroid medication, surgical removal of the thyroid glands or radioactive iodine therapy. These treatments have their limitations and side effects. For instance, anti-thyroid drugs may be difficult to administer orally, especially if they are in solid form. On the other hand, surgery is an expensive option and may be contraindicated in some cases for older subjects that could suffer from other diseases as well. Finally, radioactive iodine therapy may be administered in licensed facilities only and could require patient hospitalization.
Thioureylenes are anti-thyroid compounds used widely in the treatment of hyperthyroidism. This group of drugs includes carbimazole, methimazole, methylthiouracil and propylthiouracil. See Ginsberg J, et al., CMAJ 2003; 4, 168(5):575-585. Thioureylenes act by inhibiting the enzyme thyroperoxidase, which mediates the synthesis of T4 and T3.
At present, only thioureylene solid formulations have been approved for the treatment of hyperthyroidism in mammals. However, there is a need in the art for alternative thioureylene formulations that could improve or facilitate the treatment of this condition in patients.